ABSTRACT Support is requested for a Keystone Symposia meeting entitled B Cells and T Follicular Helper Cells ? Controlling Long-Lived Immunity, organized by Drs. Stuart Tangye, Hai Qi and Ignacio Sanz. The meeting will be held in Whistler, British Columbia from April 23-27, 2017. B cells are fundamental for the development of long-lived immunological memory following exposure to infectious pathogens and, consequently, for the success of the vast majority of currently-available vaccines. The differentiation of B cells into the effector cells of serological memory ? memory B cells and plasma cells ? occurs in germinal centers. However this process critically requires a specialized subset of CD4+ T cells termed T follicular helper (Tfh) cells. The integration of signals required to generate germinal center B cells, memory and plasma cells, and Tfh cells are strictly controlled. This is to ensure the efficient selection of antigen-specific high-affinity effector cells, and to prevent the development of immune dyscrasias associated with GCs, such as autoimmunity, immune deficiency and malignancy ? conditions that can develop when the complexities of lymphocyte differentiation in germinal centers are dysregulated. Despite the substantial advances that have been made in understanding the cellular, biochemical and molecular requirements for the generation of effective T-dependent B-cell responses, major questions regarding these processes remain. Answers to such questions are needed so as to be able to harness the intrinsic function of memory B cells, plasma cells and Tfh cells in order to enhance immunity in immunocompromised individuals, improve vaccine design and develop novel vaccines for infectious pathogens, as well as to attenuate humoral immune responses in the setting of autoantibody-mediated autoimmune diseases. This meeting will bring together basic and clinical immunologists to address unanswered questions and to discuss the latest cutting-edge breakthroughs in the biology of B cells and Tfh cells to facilitate development of new translational strategies of regulating their behavior in human immunopathologies.